Rename a file with a leading period in Windows

The short answer appears to be that Windows Explorer will not allow
you to rename a file with a leading dot. In a unix world, that'd be a
hidden file but Explorer will balk with

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Rename
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You must type a file name.
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OK
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The command line is just happy to let you rename files via mv
e.g. mv file1.txt .file1.txt

Nothing earth shattering but in the 14 years I've been using a Windows
variant, I've never run into it.